The rubro-olivary tract in the cat, as demonstrated with the method of retrograde transport of horseradish peroxidase.

The rubro-olivary projection in the cat was investigated by means of the retrograde transport of horseradish peroxidase. After injections in the inferior olive, more than a thousand labelled neurons were found in the ipsilateral red nucleus. These neurons had triangular-shaped cell bodies with an average diameter of 26.4 +/- 7.7 microns (mean +/- S.E.M.) and had few dendrites. Between 85% and 95% of the rubro-olivary neurons were found in the rostral third of the red nucleus (between A 5.5 and A 7). Morphologically, the rubro-olivary neurons are similar to rubro-thalamic neurons. Previous studies with retrograde transport of horseradish peroxidase have failed to demonstrate an extensive projection from the red nucleus to the inferior olive. These results are discussed in relation to our own findings.